1. Field of the Invention
The invention relates to liquid discharge regulators and liquid feeders for use in the medical field and the like.
Description of the Prior Art
Presently, a combination of a liquid feeder and a discharge regulator is employed to inject chemical liquids, such as antibiotics and anti-cancer drugs, into the patient's body in portions, e.g., several cubic centimeters per hour, over a long period of time. Examples of the liquid feeder are power syringe pumps, balloon infusers, and an apparatus described in the International Publication No. WO95/28977. One of the examples of the discharge regulator is described in Japanese Unexamined Patent Publication No. 9-225028 (1997). In this discharge regulator, an inlet part and an outlet part project from a casing. The inlet part is connected to a liquid feeder through a tube, and the outlet part is connected to a body connecting tube. With this construction, the liquid stored in the liquid feeder is controlled as to discharge by the discharge regulator while being injected into the body over a long period of time.
In the casing of the discharge regulator there are provided two tubes of fine (small) diameter with the same diameter and different lengths which are made of polyvinyl chloride or the like. One end of each tube is connected to the inlet part via a passage branching part, and the other end is connected to the outlet part. Thereby each tube functions as a liquid passage from the inlet part to the outlet part. A control stopper is attached to the passage branching part and it is arranged such that the liquid that has reached via the inlet part can selectively flow through a plurality of tubes of fine diameter by operating the control stopper. Therefore, the plural tubes thus arranged have different pipe losses and, by selectively changing the liquid passage with the control stopper, the discharge of the liquid flowing through the outlet part can be switched to the following three stages:
i) a first discharge obtained by injecting a liquid only through one of the tubes of fine diameter (the discharge in accordance with the pipe loss of one said tube); PA1 ii) a second discharge obtained by injecting a liquid only through the other tube (the discharge in accordance with the pipe loss of the other said tube); and PA1 iii) a third discharge obtained by injecting a liquid through both tubes (the sum of the first and second discharges).
Here, the pipe loss of a passage is determined by inside diameter and length. In the above discharge regulator, the tubes of fine diameter form a passage and their lengths are adjusted to set the pipe losses at a suitable value so as to control the discharge. Unfortunately, the inside diameter of tubes of fine diameter is subject to a certain degree of variation. Therefore, if a tube of fine diameter with a length corresponding to a predetermined pipe loss is used as it is, the desired pipe loss may not be always obtained. To this end, the following operations are performed to set a desired pipe loss. Firstly, a tube of fine diameter having a length corresponding to the pipe loss is prepared and a liquid is actually allowed to flow to measure its pipe loss (flow rate), thereby inspecting whether it is a predetermined value or not. As a result, when the obtained value deviates from the predetermined value, the length of the tube is altered and its pipe loss is measured to check whether it is the predetermined value or not. It is necessary to repeat these operations with respect to each passage. This results in one of the factors which can increase the cost of manufacture.
There is an idea of suppressing the variation in the inside diameters of tubes of fine diameter by relatively increasing the inside diameter. In this case, to obtain a predetermined pipe loss, it is necessary to increase the length of a tube of fine diameter as its inside diameter increases. This increases the size of discharge regulators. In addition, when a tube of fine diameter is housed in a casing, the tube might get bent to cause poor or no flow of liquid.
The above discharge regulator provides a three-stage switching of discharge. It is, however, desired a continuous discharge regulation to effect fine adjustment in response to the change of patient s condition and the efficacy of chemical liquids. Unfortunately, the continuous discharge cannot be effected by the conventional discharge regulators.
Although the conventional discharge regulators cannot perform continuous discharge regulation, it is possible to approach this regulation by arranging such that the discharge is switched to more stages by having more tubes of fine diameter of different pipe losses. However, in the conventional discharge regulators which require a great number of tubes of fine diameter with an attempt to the continuous discharge regulation, the cost of device increases as the number of tubes of fine diameter increases. In addition, an increase in the number of tubes increases the size of device.
Further, in the prior art, a liquid feeder and a discharge regulator are separately and independently provided, and connected by a tube. Therefore, to inject a liquid in portions into the patient's body over a long period of time, a great number of component parts are needed, which results in one of the factors increasing the cost of liquid injection. In addition, it is necessary to prepare a liquid feeder and a discharge regulator and then connect them by a tube each time a liquid injection is made. This lowers the operating performance of liquid injection.